将方法调用为主方法

Question

i know this should be very simple but i cant seem to find my mistakes, i know that its a run-time error cause when i run the program it starts asks for what conversion you want to do then you enter the number and then an error occurs. We don't do very much trouble shooting in class but..... I've tried several different things, including

public static double hourstominutes(){
    double minutes, hours;
    Scanner input = new Scanner (System.in);

    System.out.println ("Enter number of hours:  ");
    hours = input.nextInt();
    input.close();

    minutes = (double)hours * (double)60;
    return minutes;

    }

but that didnt work, i think that made it worse becuse i would have to change a whole bunch of other lines.

import java.util.Scanner;


public class TimeConverter{
public static void hourstominutes(){
    double minutes, hours;
    Scanner input = new Scanner (System.in);

    System.out.println ("Enter number of hours:  ");
    hours = input.nextDouble();
    input.close();

    minutes = (double)hours * (double)60;
    System.out.println("There are " + minutes + " minutes in " + hours + " hour(s");

    }
public static void minutestohours(){
    double minutes, hours;
    Scanner input = new Scanner (System.in);

    System.out.println ("Enter number of minutes:  ");
    minutes = input.nextDouble();
    input.close();

    hours = (double)minutes / (double)60;
    System.out.println("There are " + hours + " hours in " + minutes + " minutes");
}
public static void daystohours(){
    double days, hours;
    Scanner input = new Scanner (System.in);

    System.out.println("Enter number of day: ");
    days = input.nextDouble();
    input.close();

    hours = (double)days * (double)24;
    System.out.println("there are " + hours + " hours in " + days + "days");
}
public static void hourstodays(){
    double days; 
    double hours;
    Scanner input = new Scanner (System.in);

    System.out.println("Enter hours of day: ");
    hours = input.nextDouble();
    input.close();

    days = (double)hours / (double)24;
    System.out.println(days);
}
public static void main (String [] args){
    int option;
    Scanner input = new Scanner (System.in);

    System.out.println ("Please which conversion you would like to perform");
    System.out.println ("1. hours to minutes ");
    System.out.println ("2. minutes to hours");
    System.out.println ("3. days to hours");
    System.out.println ("4. hours to days");
    option = input.nextInt();
    input.close();

    if (option == 1){
        {hourstominutes();}
    }else if (option == 2){
        minutestohours();
    }else if (option == 3){
        daystohours();
    }else if (option == 4){
        hourstodays();
    }else {
        System.out.println("That is not a choice, enter a numerical value");
    }
}

}

i know that this is my homework and people say dont post hw but i have the whole thing done its just wrong and i dont know what to look for.

thanks ahead of time for the help Stack over flow family

Answer 1

I think it is because when you close the input object, you close the System.in as well. And when you use System.in to new a Scanner object again, you will get a java.util.NoSuchElementException . It should be better if you use a static Scanner object and close it at the very end of your program. Hope this can help you.

Answer 2

I've tested this and it works.

Couple of things..

1: Try not to make your methods all static, I know its asking you to, because you can't call a non static method from a static main, but that means you should instantiate your class, and use the object to access the methods.

2: Scanner class uses an internal buffer. You create a Scanner object in the Factory class. This Scanner reads from the underlying FileInputStream into its own buffer. the first Scanner has already consumed all the content in that FileInputStream.

A quick fix is to use the same scanner object, (ie since all your methods are using a scanner, define the scanner in the class scope:

Scanner input;
...
...
public static void main (String [] args){
input = new Scanner (System.in);
...
...

then just use input from all your methods, that will solve your problem. but do remember not to make all you methods static just cuz eclipse asked you. instantiate the class.

good luck mate :)

Tip: try to use Scanner.nextLine() in your assignments, then parse the string to a double with Double.parseDouble()

Answer 3

In your selection is easier if you use a switch statement selection = input.Text switch(selection) { case '1': hours(); break;

etc

default something(); break }